Conventionally, in the developing device used in the image forming apparatus of the electrophotographic type or the like, as a developer carrying member for feeding the developer while carrying the developer, a rotatable developing sleeve is used in many cases. At each of end portions of this developing sleeve with respect to an axial direction of the developing sleeve, a sealing member for suppressing flowing-out of the developer from a developing container is provided.
As this sealing member, an elastic member such as felt or a foam rubber is used in many cases. On the other hand, in the case where a developer having a magnetic property is used, there is a method in which a magnetic sealing member which is the sealing member formed with a magnetic member is positioned with a certain gap to an outer peripheral surface of the developing sleeve and the flowing-out of the developer from the developing container is suppressed by this magnetic sealing member. Incidentally, the developer having the magnetic property is a one-component developer (toner) in some cases, and is a two-component developer containing a non-magnetic toner and a means carrier.
The magnetic sealing member is constituted using a magnet. Further, at each of the end portions of the developing sleeve with respect to the axial direction of the developing sleeve, the magnetic sealing member extends so as to oppose a predetermined range of the developing sleeve with respect to a circumferential direction of the developing sleeve with the certain gap to the outer peripheral surface of the developing sleeve, and in this state, is mounted together with the developing sleeve to the developing container. The magnetic sealing member closes the gap between the outer peripheral surface of the developing sleeve and the surface thereof by a magnetic brush formed by erection of a chain of the developer formed along each of magnetic lines of force, and suppresses the flowing-out of the developer from the developing container.
The magnetic sealing member is in non-control with the developing sleeve, and therefore, a rotational torque of the developing sleeve becomes very small, and accordingly, it becomes possible to make a driving motor small in size and low in price. Further, also a fluctuation in rotational torque becomes small, so that rotation non-uniformity of the developing sleeve and a photosensitive drum does not readily generate, and therefore it is possible to suppress a lowering in image quality due to the rotation non-uniformity. Further, the magnetic sealing member is not deteriorated by abrasion or the like, and therefore can be used for a long term and not only contributes to lifetime extension but also is capable of meeting recycling.
Here, Japanese Laid-Open Patent Application Hei 10-39630 discloses that a magnetic sealing member is constituted by a magnet and a magnetic member and diffusion of magnetic lines of force for sealing a gap between the magnetic sealing member and a developing sleeve, in an axial direction of the developing sleeve, and a sealing property of the magnetic sealing member is improved.